创建一个不重复的随机数[重复]

Question

我想知道如何做到这一点，这样同一张图片就不会连续选择两次。可以说图片的编号为 1-3。如果选择了图片 1，那么接下来不会选择图片 1。如果选择了图片3，则可以再次选择图片1，以此类推。

我知道我必须使用while 语句，但我不知道如何使用。以下是我现在所拥有的：

- (void)chooseBackgroundImage{
  if(thisNumber % 10 == 0){
    int chooseBackgroundImage = arc4random() % 7;
    switch (chooseBackgroundImage) {
        case 0:
            backgroundImage.image = [UIImage imageNamed:@"CyanToYellowBackground.png"];
            break;
        case 1:
            backgroundImage.image = [UIImage imageNamed:@"GreenToBlueBackground.png"];
            break;
        case 2:
            backgroundImage.image = [UIImage imageNamed:@"OrangeToGreenBackground.png"];
            break;
        case 3:
            backgroundImage.image = [UIImage imageNamed:@"OrangeToPurpleBackground.png"];
            break;
        case 4:
            backgroundImage.image = [UIImage imageNamed:@"PurpleToCyanBackground.png"];
            break;
        case 5:
            backgroundImage.image = [UIImage imageNamed:@"RedToBlueBackground.png"];
            break;
        case 6:
            backgroundImage.image = [UIImage imageNamed:@"YellowToRedBackground.png"];
            break;
       }
    }
}

我也尝试过使用：

- (void)chooseBackgroundImage{
if(slogansGenerated % 10 == 0){
    int chooseBackgroundImage = arc4random() % 7;
    while(chooseBackgroundImage == oldChooseBackgroundImage){
    switch (chooseBackgroundImage) {
        case 0:
            backgroundImage.image = [UIImage imageNamed:@"CyanToYellowBackground.png"];
            break;
        case 1:
            backgroundImage.image = [UIImage imageNamed:@"GreenToBlueBackground.png"];
            break;
        case 2:
            backgroundImage.image = [UIImage imageNamed:@"OrangeToGreenBackground.png"];
            break;
        case 3:
            backgroundImage.image = [UIImage imageNamed:@"OrangeToPurpleBackground.png"];
            break;
        case 4:
            backgroundImage.image = [UIImage imageNamed:@"PurpleToCyanBackground.png"];
            break;
        case 5:
            backgroundImage.image = [UIImage imageNamed:@"RedToBlueBackground.png"];
            break;
        case 6:
            backgroundImage.image = [UIImage imageNamed:@"YellowToRedBackground.png"];
            break;
    }
    int oldChooseBackgroundImage = chooseBackroundImage
  }
}

但似乎没有任何效果。有没有办法创建一个不重复的随机数？

Answer 1

以下内容可能足以满足您的需要：

首先添加一个实例变量，比如lastChosenBackgroundImage。

之后：

int chooseBackgroundImage = arc4random() % 7;

添加：

if(chooseBackgroundImage == lastChosenBackgroundImage)
   chooseBackgroundImage = (chooseBackgroundImage + 1) % 7; // same as last time, move to next choice
lastChosenBackgroundImage = chooseBackgroundImage; // remember for next time

这确实意味着选择下一张图片的可能性是选择其他任何一张的可能性的两倍，但我怀疑这对您的用例来说不会是一个重大问题。

Answer 2

我发现你正在寻找这样的东西。

-(int)getNonRepeatedRandom{
    int randomNumber = -1;
    do{
        randomNumber = arc4random_uniform(7);
    } while (randomNumber == oldRandomNumber);
    oldRandomNumber = randomNumber; //set the random number to old random so you can check it on the next run.
    return randomNumber;
}

oldRandomNumber 必须是 iVar 才能使其工作。

您应该使用 arc4random_uniform 而不是 arc4random 模数来消除模数偏差。

Answer 3

使用此实用函数为您提供范围（在您的情况下为 0 和 6）之间的随机整数 -

#define MAX_ATTEMPTCOUNT 10
// Provides a random number between the range (both inclusive).
+ (int)randomIntegerInRange:(int)fromInt toInteger:(int)toInt excluding:(NSArray *)excludeNumbers {
    NSAssert((toInt - fromInt) > 0 && (!excludeNumbers ? YES : (toInt - (fromInt - 1)) >= [excludeNumbers count]), @"Invalid range");
    static int randomAttempts = 0;

    srandom(time(NULL));
    int randomInteger = fromInt + random() % (toInt - (fromInt - 1));

    if (excludeNumbers != nil) {
        for (NSNumber *number in excludeNumbers) {
            if ([number intValue] == randomInteger) {
                if (randomAttempts == MAX_ATTEMPTCOUNT) {
                    // Reached the maximum attempt count to get the random number but failed to find one.
                    break;
                }
                else {
                    // Recursive call to get obtain the next number.
                    ++randomAttempts;
                    randomInteger = [self randomIntegerInRange:fromInt toInteger:toInt excluding:excludeNumbers];
                }
                break;
            }
        }

        if (randomAttempts >= MAX_ATTEMPTCOUNT) {
            // Pick up the first number that's not there in visited words.
            randomAttempts = 0; // Reset the counter for next attempt.
            randomInteger = fromInt;

            for (; randomInteger <= toInt; ++randomInteger) {
                bool found = NO;
                for (NSNumber *number in excludeNumbers) {
                    if ([number intValue] == randomInteger) {
                        // Found the number.
                        found = YES;
                        break;
                    }
                }
                if (!found) break;
                else continue;
            }
        }
    }

    return randomInteger;
}

将返回的整数添加到一个数组（排除数字的数组）中，该数组实际上作为参数（excludeNumbers）传递。

如果有任何问题，请告诉我（我是为我的一个项目制作的，因此可能不完全适合您的需要，因此请随时修改或询问我）